Lamination is an important process in battery cell assembly and could improve the battery performance characteristics and the ease of handling during manufacturing. In a battery cell, gases that are generated by a variety of mechanisms could have negative effects on the cell performance and characteristics. Current prismatic cell technology (without lamination) uses mechanically applied pressure to keep interfaces intact and to force gas to the edges, a process which adds undesired weight and volume to cells. In contrast, by laminating electrodes of a cell together one can potentially minimize the negative effects of gases by forcing them to the edges of the stack instead of allowing them to form interlayer bubbles and thereby increase interfacial resistance (especially important for prismatic cells). In addition, a properly laminated interface will often have lower impedance (resistance) than one which is not laminated, and would thereby improve the power characteristics of said cell. Secondly, great care needs to be taken to maintain the alignment of electrodes in a prismatic cell during the assembly process. By laminating the entire stack together into a monolithic entity during and/or immediately after stacking, the cell is less susceptible to misalignment in subsequent assembly steps.
Separator layers are important components of batteries. These layers serve to prevent contact of the anode and cathode of the battery while permitting electrolyte to pass there through. Additionally, battery performance attributes such as cycle life and power can be significantly affected by the choice of separator. For example, U.S. Pat. No. 5,587,253, assigned to Bell Communications Research Inc., discloses a soft polyvinylidene fluoride (PVdF)-HFP copolymer that has been highly plasticized for use as a binder in a composite separator. While the use of a softer composite separator may provide for gentler lamination conditions, the mechanical properties of the layer are degraded, resulting in other compromises and trade-offs to the cell.
Inorganic composite materials have also been used in separator layers. Such composite separators include a silica, alumina, TiO2 (or other ceramic) filler materials and a polymer binder. The filler and binder may be blended and extruded to form a composite sheet and any volatile components are removed by extraction or evaporation to form a porous body. Other examples blend the filler and binder to form a mixture that is applied to a substrate by various coating means, such as doctor balding, roll coating or screen, stencil printing or gravure. The compositions of the polymer-inorganic separators affect the properties of resulting separator layers and the characteristics of the cell. Polymer-rich separator layers, while easier to laminate and providing better lamination strength, frequently result in less porosity, increased resistance, and lower conductivity. In contrast, inorganic filler-rich separator layers frequently have higher porosity and better conductivity, but are generally more difficult to laminate and result in lower lamination strength, under conditions which minimize damage to the cell.
Thus, there is a need for inorganic material-polymer separator materials that are easy to laminate and have good lamination strength, porosity and conductivity.